1. Field of the Invention
The present invention relates to an electrophotographic image-forming apparatus, and more particularly to the construction in an image-forming apparatus of a guide mechanism for guiding a printhead with respect to a print process cartridge.
2. Description of the Related Art
FIG. 21 is a perspective view of a conventional electrophotographic image-forming apparatus.
The conventional apparatus includes a rotatable lid 1 and a stationary main body 3. The lid 1 is pivotally mounted to the main body 3 so that the lid 1 can be opened and closed relative to the main body 3. The main body 3 incorporates a print process cartridge 7 having a photoconductive drum, not shown. There is provided an operating panel 3a at the front end of the main body 3. Operating buttons and other controls, not shown, are provided on the operating panel 3a. Shafts 4 are provided at the rear end portions of opposed side walls of the main body 3 and extend toward each other into bearing holes 2 formed in the end portion of the lid 1. Thus, when the lid 1 is rotated in a direction shown by arrow A, the lid 1 closes the opening of the main body 3. A printhead assembly 6 having a printhead 5 therein is attached to the forward underside of the lid 1. The printhead 5 is loosely held in the printhead assembly 6 so that the printhead 5 is movable to some extent within the printhead assembly 6.
When the lid 1 is rotated in the direction shown by arrow A, the printhead 5 moves along an arcuate path into mating engagement with the print process cartridge 7. The printhead 5 is formed with projections 5a at longitudinal end portions thereof. The print process cartridge 7 is formed with recesses, not shown, which receive the projections 5a. When the lid 1 closes the main body 3, the projections 5a completely fit into the recesses in the print process cartridge 7, so that the printhead 5 is accurately positioned with respect to the photoconductive drum in the print process cartridge 7.
The printhead assembly 6 incorporates a compression spring, not shown. When the printhead 5 is fitted into the print process cartridge 7, the compression spring urges the printhead 5 against the print process cartridge 7, thereby preventing the printhead 5 from rattling. Pressing the printhead 5 against the print process cartridge 7 holds the printhead 5 at an accurate position relative to the photoconductive drum, thereby ensuring good print quality.
The operation of the aforementioned conventional image-forming apparatus will be described.
The compression spring urges printhead 5 outwardly from the printhead assembly 6 such that the printhead 5 is resiliently movable in the printhead assembly 6. When the lid 1 is opened, the printhead 5 abuts part of the printhead assembly 6. When the lid 1 is closed, the printhead 5 first engages the print process cartridge 7 and is pushed back by the print process cartridge into the housing of the printhead assembly 6 against the urging force of the compressed spring, so that the spring is further compressed.
The compression spring is compressed more when the lid 1 is closed than when the lid 1 is opened. Thus, the position of the printhead 5 when the lid 1 is opened differs from that when the lid 1 is completely closed.
Therefore, it is necessary to precisely adjust the position of printhead 5 with respect to the printhead assembly 6 after the projections 5a of the printhead 5 are fitted into the recesses formed in the print process cartridge 7.
Thus, the orientation of the printhead 5 must be gradually changed in accordance with the rotation of the lid 1 so that while the lid 1 rotates in the arcuate path, the projections 5a are properly received into the recesses in the print process cartridge 7. The housing of the printhead assembly 6 must be shaped, taking into consideration where in the arcuate path of the printhead 5 the print process cartridge 7 receives the printhead 5. Thus, the housing has a complicated shape and must be manufactured with a high level of dimensional accuracy.
If the housing of the printhead assembly 6 is shaped such that the orientation of the printhead 5 gradually changes as the lid 1 rotates, the compression spring may urge the printhead 5 in directions that are different from the orientation of the printhead 5 depending on the rotational position of the lid 1. The printhead 5 may not be smoothly oriented according to the shape of the housing. A similar problem occurs when the compression spring has not enough biasing force.
In an attempt to solve the aforementioned problems, the compression spring maybe other shapes, e.g., a cone-shaped spring, than an ordinary cylindrical coil spring. Further, springs having low spring constants or long springs may be used. However, springs of complicated shapes will be expensive.